Electric switchboards are divided vertically into compartments, each of which is generally associated with a consumer and through which extends a three phase supply line from which are branched off busbars carrying the voltage to the various consumers. Between the main busbars and the line are disposed circuit breakers, isolators and other measuring, protection and like devices.
For maintenance, inspection and repair purposes one or more parts of a compartment can be removed after only the compartment in question has been isolated and put out of action, so that access can be gained to the various parts of the compartment concerned.
It has recently been proposed to fill the compartments with an insulating gas at low pressure, particularly with sulfur hexafluoride (SFs), in order to gain certain advantages over switchboards at present in use, including a reduction of the dimensions of the switchboard, insensitivity of components to the environment, and the elimination of fire hazard. The use of SFs or other gas under pressure nevertheless entails various problems when inspection, maintenance and test operations have to be carried out. In such cases it is in fact necessary to evacuate the compartment, with the consequence that the entire switchboard is put out of action, since the switchboard by itself, without the gas, no longer dependably provides the operating conditions for which it was designed.
Putting the switchboard out of action is particularly burdensome because it means that stations or plants will be inoperative even for simple periodic supervisory measures, which of course are essential for safety reasons. Access to various parts of the switchboard also becomes complicated because the indispensable leaktight construction of the compartment makes the removal and/or separation of parts more difficult.
Consequently, known switchboards utilizing a gas as insulant have disadvantages and limitations which impede their wider generalized use.